Dielectric heating apparatus preferably for heating gas-porous material



Oct. 28, 1952 WADE 2,615,259

DIELECTRIC HEATING APPARATUS PREFERABLY FOR HEATING GAS-POROUS MATERIALFiled Feb. 28, 1950 Fig.l.

00000000000 0 000000000000 000000000000 0'0 0 O OO 0 OO O O O000000000000 000000000000 OOOOOOOOOOOOO INVENTOR Morion E.W0de.

ATTORNEY Patented Oct. 28, 1952 DIELECTRIC HEATING APPARATUS PREF-ERABLY FOR HEATING GAS-POROUS MA- A TERIAL Marion E. Wade, Kansas City,Kans., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application February 28, 1950, SerialNo. 146,678

9 Claims. (Cl. 34--1) My invention is directed to improvements fordielectric heating materials of a type which give off a gas or vaporduring such heating, although my invention may have broader uses.

An object of my invention is to provide a simple economical and ruggedapparatus for dielectrically drying a mass of material while air orother gas is passed through the mass for removing vapors or gases thatmay be produced during the dielectric heating, or for aiding the heatingof the material, or for any other purpose. An important ancillary objectis dielectrically to heat the material as aforesaid so that the heatingis uniform throughout the mass, within tolerable limits.

A further object of the invention is to pro-- vide apparatus fordielectrically heating granular material or the like which can becontinuously fed to the apparatus for heat-treatment and con tinuouslyremoved therefrom after the heattreatment.

A further object of my invention is to provide an apparatus having apair of heating-electrodes between which material is dielectricallyheated, the apparatus having means which passes a hot air-stream betweenthe heating-electrodes and through the material for one or more purposessuch as to carry away gases and moisture given off by the materialduring the heating period, or toequalize the temperature gradient of thematerial between the heating-electrodes, or to help supply heat lossesdue to radiation and convection, or to safeguard against overheating.

In accordance with my invention I provide two upstanding concentricheating-electrodes each of which is formed of perforated metal orscreening. The heating-electrodes are relatively insulated and ahigh-frequency electric field is established in the annularwork-receiving space between them by any suitable means. The material tobe heated is fed into the top of this annular work-receiving space andremoved continuously from the bottom. A hot air-stream is caused to flowthrough the heating-electrodes and material; and, in accordance with animportant feature of my invention, this hot airstream moves generallyradially through the material from the outside inwardly. The tem- 2conjunction with the accompanying drawing, in

which:

Figure 1 is a vertical sectional view centrally through apparatusembodying my invention; and

Fig. 2 is a horizontal sectional view substantially on the line II--IIof Fig. 1. v

The preferred apparatuscomprises on outer tubular member which isreferred to in its entirety by the reference numeral 2, and an innertubular member which is referred to in its entirety by the referencenumeral 4.

The outer tubular member 2 comprises, in endto-end relation, aperforated heating-electrode 6 having a circular cross-section, anupwardly tapered tube-section 8 and an upright cylindrical tube-sectionliJ. Below the heating-electrode 6, the other tubular member 2 comprisesa downwardly tapered tube-section l2 and a tubular tube-section I lextending downwardly therefrom. All sections are metallic and all,except the heating-electrode 8, have solid walls.

The inner tubular member 4 comprises, in endto-end relation, an innerperforated heatingelectrode 16 having a circular cross-section, anupwardly tapered tube-section [8, an insulating tube-section 20,preferably of quartz or the like,

, and an exhaust duct-section 22 that passes out perature of theair-stream is controlled so that of the section 10 of the outer tubularmember 2.

Below the inner heating-electrode IS, the inner tubular member 4comprises a downwardly tapered tube-section 24 terminating in a flatclos ing apex portion 28. All sections of the inner tubular member 4,except the heating-electrode [6, have solid walls, and all, except theinsulating section 20, are metallic.

The inner tubular member 4 is supported by insulating means 30 attachedto the apex portion 26. The insulating means 30 is carried on aninsulator structure 32 securedly fixed to the tube-section I l of theouter tubular member 2. Preferably, the inner tube-sections I8 and 24taper at greater angles than their opposite facing tube-sections 8 andI2, respectively.

The heating-electrodes 6 and I6 are nested or concentric and provide anannular-like work-receiving space 34. A plurality or small distributedinsulating spacers 36, of a material such as quartz, is secured to theheating-electrodes 6 and It so as to keep them suitably spaced,preferably at a uniform distance apart. High-frequency energy isdelivered to the work-receiving space 3-4 between the heating-electrodesby any suitable means shown as a coaxial-transmission line 38 having anouter grounded conductor 40 seaeiazso cured to the metallic section I2of the outer tubular member 2, and an insulated conductor 42 thatconnects to the metallic section 24 of the inner tubular member 4. Atube-oscillator generator 44 feeds high-frequency energy to thetransmission line 38.

Material to be heat-treated is fed at a controlled rate into the top ofthe upper section In of the outer tubular member 2 by any suitablemeans, such as a hopper. The material drops through this upper section land passes downwardly through the space between the tapered members 8and I8 and into the work-receiving space 34. Most of the heating-ofthe-material takes place in this space 34, although-a slight preliminaryheating of the material can be made to occur in the space between thetapered upper tube-sections 8 and I8. After heating, thematerial passesthrough the lower tubular section 12 in a well-understood manner, to anysuitable receptacle or other work-receiving means.

In the operation of the apparatus described,

the electric field provided is preferably such that by the time thematerial reaches the lower part of the work-receiving space 34 it is atsubstantially the desired temperature. The electric heating, however, isaugmented by a heated airstream which is fed to the work-receiving space34 in an inward radial direction. For this purpose, an outer metallicduct 46 is placed around the outer heating electrode'fi, the ductcomprising a scroll-wall 48, a top wall 50, a bottom wall 52,

and an inlet duct-section 54 connected to the largest part of thescroll. Air is fed to the inlet duct 54 by a fan 56, the air passingthrough heatradially nearer the inner heating-electrode l6 than it is ata point farther therefrom. Consequently, there will be a temperaturegradient radially through the material in the work-space 34. By forcingthe hot air from the outside inwardly, a balance can be'made between theelectrical heating so that the temperature gradient is made more uniformacross the width of the maj terial.

While the apparatus described is obviously of general application, it isrecommended for heating granular material. The activation of silica gelis an example of such material. For such use, 'the work-receiving spacecan be about one inch wide, and have a voltage gradient thereacross ofabout 3,000 volts per inch maximum so as to avoid excessive-arcing, thevoltage source having the frequency of 30 megacycles per second. For

such application, it is recommended that the air vsuppliedto the scroll48 be at about 1300 F., and the; rate of air-flow controllable.

While I have described my invention in a form 'nowpreferred, it isobvious that its principles are jof;;general a plication for many uses,and that the specific embodimentherein described is subject to widemodification.

I claim as my inventioni A 1. Dielectric heating apparatus of a typeolescribed comprising a pair of relatively insulated tubular upstandingheating-electrodes, each of said heating-electrodes being perforatedacross its surface, said heating-electrodes being nested with radialspacing to provide a work-heating space therebetween, means forsupplying highfrequency energy to said heating-electrodes, and means forfeeding work to be heated to said work-heating space, a fluid mediumsupply member positioned on one side of a first of saidheating-electrodes, said fiuid medium supply member surrounding saidfirst heating-electrode, and a fluid medium exhaust member positionedadjacent the other of said heating-electrodes to remove said fluidmedium from the side of the lastsaidheating-electrode which is oppositesaid first heating-electrode.

2. Dielectric heating apparatus of a type described comprising a pair ofrelatively insulated tubular heating-electrodes, each of saidheatingelectrodes being perforated across its surface,saidheating-electrodes being nested with radial spacing to provide awork-heating space therebetween, means for supplying high-frequencyenergy to said heating-electrodes, means for feeding'work to be heatedto said work-heating space, a duct connected to the space inside theinner of said heating-electrodes, and an outer duct about the outer ofsaid heating-electrodes, fluid medium supply means positioned on oneside of said Workheating space, said fluid medium supply meanssurrounding said space, and fluid medium exhaust means positionedadjacent the opposite sideof said Work-heating space and adapted toremove said fiuid medium from the last-named side of said space.

3. Dielectric heating apparatus of a type described comprising a pair ofrelatively insulated tubular heating-electrodes, each of saidheatingelectrodes being perforated across its surface, saidheating-electrodes being nested with radial spacing to provide awork-heating space therebetween, means for supplyinghigh-frequency'energy to said heating-electrodes, means for feeding workto be heated to said work-heatingspace, and an exhaust duct connected tothe'space inside the inner of said heating-electrodes; and fluid mediumsupply means positioned adjacent the work-heating space to force thefluid'medium through said space in a direction perpendicular to thedirection of movement of the work through said space.

4. Dielectric heating apparatus of a type described comprising apalr ofrelatively insulated tubular heating-electrodes, each of saidheatingelectrodes being perforated across its surface, saidheating-electrodes being nested with radial spacing to provide awork-heating space therebetrodes, support means carrying saidheating-electrodes so that they are upstanding and nested with radialspacing to provide a work-heating 6 Dielectric heating apparatus of atype described comprising a pair of tubular members comprisingheating-electrodes, support means carrying said heating-electrodes sothat they are upstanding and nested with radial spacing to provide awork-heating space therebetween, said support means comprisinginsulating means insulating the inner of said heating-electrodes fromthe outer of said heating-electrodes, said outer heating-electrode beinggrounded, said heating-electrodes having perforated surfaces, 2. solidwall duct extending from an upper end of said inner heating-electrodes,said duct comprising an insulating section, and an insulated powersupply conductor electrically connected to the other end of said innerheating-electrode.

7. Dielectric heating apparatus of a type described comprising a pair oftubular members comprising heating-electrodes, support means carryingsaid heating-electrodes so that they are upstanding and nested withradial spacing to provide a work-heating space therebetween, saidsupport means comprising insulating means insulating the inner of saidheating-electrodes from the outer of said heating-electrodes, said outerheating-electrode being grounded, said heatingelectrodes havingperforated surfaces, a solid wall duct extending from the upper end ofsaid inner heating-electrodes, said duct comprising an insulatingsection, means for feeding work to the upper end of said work-heatingspace, and means for removing work from the lower end of saidwork-heating space.

8. Dielectric heating apparatus of a type described comprising a pair oftubular members comprising heating-electrodes, support means carryingsaid heating-electrodes so that they are upstanding and nestedwithradial spacing to provide a work-heating space therebetween, saidsupport means comprising insulating means insulating the inner of saidheating-electrodes from the outer of said heating-electrodes, said outerheating-electrode being grounded, said heatingelectrodes havingperforated surfaces, an exhaust duct extending from an upper end of saidinner heating-electrode, said duct comprising an insulating section, anouter supply d'uct'about said outer heating-electrode, means for.forcing hot gas through said outer supply duct for passage through saidwork-heating space to said exhaust duct, and means for applyinghigh-frequency power across said heating-electrodes.

9. Dielectric heating, apparatus of a type described comprising a pairof tubular members comprising heating-electrodes, support means carryingsaid heating-electrodes so that they are upstanding and nested withradial spacing to provide a work-heating space therebetween, saidsupport means comprising insulating means insulating the inner of saidheating-electrodes from the outer of said heating-electrodes, saidheatingelectrodes having perforated surfaces, and a solid wall ductextending from the upper end of said inner heating-electrode, said ductcomprising an insulating section, an insulated power supply conductorconnected to said inner heating-electrode, an outer supply duct aboutsaid outer heatingelectrode, and means for forcing hot gas through saidouter supply duct for passage through said work-heating space and thento said exhaust duct, said tubular members having a work-receiving upperend leading to said work-heating space, and a work-leaving lower end.

MARION E. WADE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES" PATENTS Number Name Date 1,424,565 Goskar Aug. 1, 19221,993,843 Kaelin Mar. 12, 1935 2,483,623 Clayton Oct. 4, 1949 2,489,135Himmel et a1. Nov. 22, 1949 FOREIGN PATENTS Number Country Date 621,099Great Britain Apr. 4, 1949

